Bug 1381802 - [mach] Ensure subcommand help is displayed whenever a subcommand and --help are specified, r=gps
After this patch, the following will all display the subcommand help where they previously displayed
the command help:
$ mach help <command> <subcommand>
$ mach <command> --help <subcommand>
$ mach <command> <subcommand> --help
The command help will still be shown for:
$ mach help <command>
$ mach <command> --help
MozReview-Commit-ID: 7EsVblnCaFM